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Brain & Behaviour > Week 1 - Peripheral Nervous System > Flashcards

Week 1 - Peripheral Nervous System Flashcards

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1
Q

How are the different gradations of intensity transmitted?

A
  1. Frequency coding (temporal summation) - increasing the firing rate.
  2. Population coding (spatial summation) - increasing the number of parallel fibres that transmit information.
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2
Q

What is adaptation with respect to nerve stimulation?

What are examples of slow-adapting sensory receptors?
Fast adapting?

A

Adaptation: the intensity of a signal diminishes if the signal persists for a long time.

Slow adapting = Merkel cells and carotid bodies.
Fast adapting = Pacinian corpuscles.

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3
Q

What is lateral inhibition?

A

When a point is stimulated, neurons directly below point dampen the signal from adjacent neurons thus blocking the lateral spread of the signal.

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4
Q

What are the 4 elementary attributes of a stimulus?

A
  1. Modality/type
  2. Intensity
  3. Duration
  4. Location
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5
Q

What is a receptor/generator potential?

A

A depolarization of the receptive portion of the sensory axon generated by a sensory stimulus.

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6
Q

What nerves carry information on taste?

A

CN VII & CN IX

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7
Q

Somatic sensations can be divided into two groups - what are they?

A
  1. Exteroreceptors (sense change in external stumulus)

2. Interoceptors & Proprioceptors (provide info on body position)

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8
Q

Give an example of a interoreceptor/proprioceptor.

A

Ruffini’s corpuscle - sensitive to stretch of the skin; also senses position/mvmt)

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9
Q

Give examples of an exteroreceptor & briefly state what type of stimulus is detected by each of them.

A
  • Pacinian corpuscle (deep pressure, vibration)
  • Meissner corpuscle (light touch)
  • Free nerve endings (pain, temperature, touch, pressure, stretch)
  • Merkel disk (low frequency vibration)
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10
Q

What is neurulation? When does it occur?

Describe the process.

A

Formation, folding, and closure of the neural tube during the 3rd wk of development.

  • the closure begins in the cervical region
  • SHH stimulates the initial folding in of the neuroectoderm (ectodermal plate)
  • as it folds, the borders of the neural plate become the neural crest cells
  • the anterior neuropore closes at day 25 post fertilization
  • the posterior neuropore closes 27 days post fertilization
  • closure creates a lumen
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11
Q

In the development of the spinal cord, what determines the differences between doral and ventral? Briefly describe.

A

Concentration gradients and signalling cascades:

Dorsal edge = “roof plate”

  • high concentration of BMP
  • dorsal half of spine (Alar Plate) develop into sensory neurons

Ventral edge = “floor plate”

  • high concentration of SHH
  • ventral half of spine (Basal Plate) develops into motor neurons

Roof/Floor plates do not have any viable neurons.

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12
Q

What are the layers of the neural tube cell population that arise when the neuroepithelial cells proliferate?
(Start at lumenal side)

A
  1. Ventricular layer - very few nuclei
  2. Intermediate (Mantle) layer - thickest layer, lots of nuclei, develops into gray matter
  3. Marginal layer - develops into white matter of spinal cord
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13
Q

What happens when the neural tube fails to close?

A

Spina bifida:

  • occulta (mild)
  • cystica (mod) –> meningocele or meningomyelocele
  • myeloschisis (severe) –> entire neural tube is open posteriorly
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14
Q

What embyological layer are keratinocytes derived from?

- what about melanocytes?

A

keratinocytes –> ectoderm

melanocytes –> neural crest cells

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15
Q

What is the etiology of neural tube defects?

A

Multifactorial:

  • hyperthermia
  • Valproic acid
  • excessive Vit A intake
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16
Q

What is the best way to prevent neural tube defects?

A

Folic Acid intake, 0.4mg/day, before and during pregnancy

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17
Q

How are neural tube defects diagnosed?

A

US (8-10 wks)

AFP (maternal serum & amniotic fluid)

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18
Q

Describe the segmentation of the brain and state what each portion develops into.

A
  1. Prosencephalon (Forebrain) –> Telencephalon (cerebrum) & Diencephalon (thalamus, hypothalamus, pineal, post pituitary)
  2. Mesencephalon (Midbrain)
  3. Rhombencephalon (Hindbrain) –> Metencephalon (pons/cerebellum) & Myelencephalon (medulla)
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19
Q

What are the flexures of the brain?

A

Ventral flexures (at 5th wk):

  • Cervical (brain-spinal cord jxn)
  • Cephalic (midbrain)
Dorsal flexure (at 7th wk):
 - Pontine (hindbrain)
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20
Q

How does the pontine flexure affect the development of the brain?

A

It thins the roof plate and causes rearrangement of the Alar-Basal plates from a dorso-ventral pattern to a latero-medial pattern.

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21
Q

What is Wallerian degeneration?

A

Occurs after complete laceration of a neuron - the axonal section distal to the laceration will degenerate over a short time.

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22
Q

What is the body’s response to nerve cell laceration?

A

The proximal end of the lacerated axon makes growth cones and starts regenerating.

  • sends out sprouts to search for neural tissue or laminin (which triggers regeneration)
  • if the distal axon is found, the axon can follow that path to regenerate itself
  • if the distal axon/neural tissue is not found, the proximal axon keeps sending out sprouts and may create scar tissue and develop a neuroma
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23
Q

When the laceration is surgically reattached, what happens if the ends are not trimmed prior to joining them together?

A

Can get scarring and neuroma formation.

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24
Q

What is carpal tunnel syndrome?

A

Compression of the median nerve at the base of the hand - get tingling/weakness/numbness in median nerve distribution

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25
Q

What is neurapraxia?

A

Temporary loss of sensory/motor nerve function due to nerve compression block in the peripheral nervous system.
- causes increased latency

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26
Q

What is the management of carpal tunnel syndrome?

A

Splinting and activity modification - goal is to provide largest volume in carpal tunnel to reduce compression of the nerve

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27
Q

What are microglia?

A

Macrophage cells in the brain

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28
Q

What is the name for stem cells in the brain?

- what can these develop into?

A

Polydendrocyte

- can develop into astrocytes, oligodendrocytes, or neurons

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29
Q

Where are bipolar neurons found?

A

retina

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30
Q

What does a nerve contain?

A

It is a bundle of fascicles containing many axons

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31
Q

What is an alpha motor neuron?

A

A motor nerve that directly innervates extrafusal muscle fibres (skeletomotor)

32
Q

What is a gamma motor neuron?

A

A motor neuron that innervates intrafusal muscle fibres & helps keep the muscle spindle taut while the muscle is contracting.

33
Q

Where are upper motor neurons?

A

They have their cell body in the motor cortex or brainstem.

- innervate lower motor neurons.

34
Q

Where are lower motor neurons?

A

Cell bodies in spinal cord (anterior horn)

- directly innervate muscle fibers

35
Q

What are the sensory receptors in muscle?

A
  • Muscle spindles

- Golgi tendon organs

36
Q

What types of muscle have a higher density of muscle spindles?

A

Muscles that are used for fine motor tasks (ex. hand muscles)

37
Q

What is the role of the muscle spindle?

A

It informs brain about muscle length and velocity of contraction.

38
Q

What are the three types of intrafusal muscle fibres?

A
  • Bag1 (largest)
  • Bag2
  • Chain fiber* (contains a row of nuclei)

There are 4 chain fibers (and one of each bag fiber) in each spindle.

39
Q

What is the sensory innervation to muscle spindles?

A
  • Group Ia afferents (annulospiral ending; Bag1, bag2, & chain fibers) –> sensitive for detecting change
  • Group II afferents (unmyelinated spray terminals; Bag2 & chain fibers) –> give info on length
40
Q

What is the motor innervation to muscle spindles?

A

Gamma (fusimotor) neurons:

  • static (bag2 & chain)
  • dynamic (bag1)
41
Q

What information is gained from Group II afferents?

A

Length

42
Q

What information is gained from Group Ia afferents?

A

Velocity & Length

43
Q

How does muscle stretch affect the muscle spindle?

A

Sensory neurons around spindle fire when it gets stretched

- stretch-operated cation channels lead to AP generation

44
Q

What property does the action of dynamic gamma-motor neurons affect?

A

Velocity sensitivity

45
Q

What property does the action of static gamma-motor neurons affect?

A

Length sensitivity

46
Q

When are spindle sensory neurons firing?

A

They are tonically active - fire APs when muscle is at resting length
- results in muscle tone (from tonic excitation)

47
Q

Describe the Hoffmann Reflex (the stretch reflex without stretch).

A

Peripheral nerve is stimulated.

  • sends impulse down motor portion to stimulate muscle (M-wave)
  • sends impulse up sensory portion, through spinal cord, back down motor to stimulate muscle (larger, H-reflex)
48
Q

What is a myotatic unit?

A

A connection of nerve pathways controlling a single joint.

49
Q

What is reciprocal inhibition?

A

Relaxation of the opposing muscle during contraction of the agonist.

50
Q

What type of lesion can causes flaccid paralysis?

A

Lower (alpha) motor neuron lesion

51
Q

What does an upper motor neuron lesion present with?

A 
Spastic paralysis (ie. reflex is intact, but patient has weakness and difficulty controlling muscles).
 - may also show Babinski's sign
52
Q

What types of neurons are found in a peripheral nerve?

A
  • somatic motor
  • somatic sensory
  • autonomic (visceral motor/sensory)
53
Q

Describe the classification schemes for the peripheral axon.

A

Based on conduction velocity (usually describes motor neurons):
- A (fastest, largest diameter, myelinated) –> B (myelinated) –> C (slowest, unmyelinated)

Based on diameter (exclusively for sensory neurons):
- I (largest, fastest) –> II –> III –> IV (smallest, slowest, unmyelinated)

54
Q

What is the basal lamina in peripheral nerve axons?

- what is it required for?

A

It is ECM (mainly type IV collagen) that surrounds the individual axon and myelin.
- contains laminin & fibronectin which interact with growth cone adhesion molecules needed to guide axon sprouts in axonal regeneration.

55
Q

There are two types of Schwann cells. What are they?

A
  1. Myelinating (covers segments of axon)

2. Ensheathing (covers entire length of axon)

56
Q

Do type C fibers have Schwann cells?

A

Yes! but the schwann cells do not produce myelin

57
Q

What is neurapraxia?

A

Grade I Injury - Segmental Demyelination (mildest form of nerve damage)
- causes conduction block (temporary loss of motor/sensory innervation)

58
Q

What happens when there is complete demyelination of a segment of an axon?

A
  • slower AP

- Na+ channels redistribute themselves away from nodes of Ranvier

59
Q

What factors are needed for remyelination?

A

Trophic factors & cytokines released by damaged Schwann cells and affected axons –> causes proliferation of undifferentiated Schwann cells

60
Q

What does the amplitude (of waves in an EMG recording) give you information about?

A

Number of neurons activated

61
Q

What does the latency (of waves in an EMG recording) give you information about?

A

The conduction velocity (if the path length is known)

62
Q

What is CMAP (Compound Muscle Action Potential)?

A

An EMG investigation whereby an M-wave is generated (during muscle contraction) by peripheral stimulation of alpha motor neurons

63
Q

What is axontmesis?

A

Grade II Peripheral Axon Degeneration:

  • Disruption of nerve cell axon & myelin sheath
  • no damage to schwann cell, endo/peri/epineurium
  • Wallerian degeneration
64
Q

What is neuorntmesis?

A

Grade III Peripheral Axon Degeneration:

  • both the nerve and nerve sheath are damaged
  • only partial recovery is possible
65
Q

What growth factor is released at the growth cone in Wallerian degeneration?
- what is it responsible for?

A

Neuroregulin

- initiates Schwann cell dedifferentiation & proliferation

66
Q

What is allodynia?

- what is another name for this?

A

Allodynia (aka dysesthesia) = pain evoked with a normally non-painful stimulus

67
Q

What is hyperalgesia?

A

Hyperalgesia = extra pain evoked with a normally painful stimulus

68
Q

How are reflexes affected by Upper vs Lower MN neuropathy?

A

UMN –> hyperreflexia & increased tone

LNM –> Hyporeflexia, decreased tone, & atrophy

69
Q

What is the difference in presentation of nerve root damage versus peripheral nerve damage?

A

Peripheral nerve damage has a more discrete margin around the affected area.

70
Q

What are the features of axonal neuropathy?

A
  • usually affects sensory neurons
  • slowly progressive
  • length dependent
  • loss of ankle jerks
71
Q

What are the features of demyelinating neuropathy?

A
  • affects mainly motor but also sensory neurons
  • rapid
  • arms & legs
  • areflexia
72
Q

What is an example of axonal neuropathy?

A

Diabetic neuropathy

73
Q

What is an example of demyelinating neuropathy?

A

Guillain-Barre syndrome

74
Q

What diagnostic tests should be ordered to diagnose peripheral neuropathy?

A
  • Blood work (CBC, glc, TSH, Renal & liver panels, Vit B12, VDRL, HIV, Lyme, Connective tissue screen, serum immunoelectrophoresis)
  • EMG
  • Lumbar puncture (if thinking GBS)
  • Heavy metal analysis
  • Nerve bx
75
Q

What type of neuropathy is suggested by an EMG showing decreased amplitude?
- what about increased latency?

A

Decreased amplitude ==> Axonal

Increased latency ==> Demyelinating

Brain & Behaviour (4 decks)

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